# Fibonacci function/Subroutine Using C Programming Language

In this sample C programming assignment a subroutine asuAdd is given. Students are required to write a function in C Programming language using the subroutine asuAdd to calculate huge Fibonacci numbers.

The prototype/signature for the function is given as follows : –

n is the Fibonacci number that needs to be calculated. The series of Fibonacci number starts from values 0, 1; and n is to be calculated.

#### SOLUTION : –

#include

#define MAX_SIZE_TEST 1000

typedef unsigned int bigNumTest[1 + MAX_SIZE_TEST];

typedef unsigned int bigNumN[];

int asuAdd(bigNumN bigN0P, const bigNumN bigN1P, unsigned int maxN0Size);

void halt()

{

}

/*

* function: asuFibonacci

*

* n is the Fibonacci number that you would like to calculate. (Our Fibonacci

* numbers start with f0 = 0, f1 = 1, etc., and we would like to calculate fn.)

*

* The return value of the function is either n, or the largest Fibonacci number

* that could be accurately calculated before overflow occurred.

*

* maxSize is an integer that specifies how many valid words can be stored in the

* bigNumN numbers.

*

* bNP is a pointer to a pointer to a bigNumN number holding the Fibonacci number

* indicated by the return value. bNP will either point to static array bNa or

* static array bNb.

*

*/

int asuFibonacci(int n, int maxSize, bigNumN **bNP) {

// **** modify below and fill in code and ensure proper operation including return value. ***

static bigNumTest bNa = {1,0,0}; // initial fibonacci (0) = 0

static bigNumTest bNb = {1,1,0}; // initial fibonacci (1) = 1

int i;

if (n == 0)

{

*bNP = &bNa;

return 0;

}

else if (n == 1)

{

*bNP = &bNb;

return 1;

}

*bNP = &bNb;

for (i = 2; i <= n; i++)

{

if (!(i % 2)) // If it’s even

{

if (asuAdd( bNa, bNb, maxSize))

{

// if overflow, return last i

n = i – 1;

break;

}

*bNP = &bNa;

}

else // if it’s odd

{

if (asuAdd( bNb, bNa, maxSize))

{

// if overflow, return last i

n = i – 1;

break;

}

*bNP = &bNb;

}

}

return n;

}

int main() {

bigNumN *fibResP = NULL;

int i = asuFibonacci(1000000, MAX_SIZE_TEST, &fibResP);

halt();

return i;

}

// or move this to the assembly file

void _exit(int status) {

volatile int x; // work around problem with xilinx system debugger.

loop:

x++;

goto loop;

}